Typically, conventional incinerators for burning residential and industrial waste matters are classified into three types: a stoker type, a fluidized bed type and a rotary kiln type. Among them, the stoker type incinerator is generally utilized. The stoker type incinerator has grates arranged in multi-steps in an incinerator, wherein waste matters to be burned are incinerated while being moved along the grates.
There is a need to cool down the grate in order to increase the life span of the grate, which places and burns waste matters thereon, and to reduce the amount of pollutants that result from imperfect combustion. To cool a grate, an air-cooling type or a water-cooling type is generally employed. The air-cooling type resorts to a cooling method wherein the grate is cooled and waste matters are burned by feeding air for combustion from underneath the grate. The water-cooling type utilizes a cooling method wherein cooling pipes are equipped in/on the grate and the grate is cooled by means of cooling water flowing through the cooling pipes so as to prevent high temperature corrosion, which is a serious drawback of the air-cooling type.
Japanese Patent Laid-Open Publication No. 2000-240926 discloses a water-cooled grate, wherein U-shaped pipes are provided at the front face of the grate. Also, Korean Patent Laid-Open Publication No. 2002-0091022 discloses a fixed type water-cooled combustion grate, wherein cooling water circulates along blocking plates placed inside the grate to cool off the grate.
However, in case of the above water-cooled grates, when the amount of waste matter is decreased in a partial-load operation of an incinerator or a thermal load of the incinerator becomes reduced just before shutting down the incinerator, the cooling water overcools the grate. Thus, the surface temperature of the grate drops below a prescribed point. Among various combustion gases, substances containing corrosive components then condense on the surface of the grate. As such, low temperature corrosion occurs on the surface of the grate. Such low temperature corrosion typically leads to increased costs associated with grate maintenance and pollutant control.
Further, in order to prevent overcooling of the grate by means of cooling water, a procedure of controlling the flow rate or the temperature of cooling water may be applied. However, such procedure is difficult to implement since the surface of the grate cannot be properly controlled. Accordingly, there is a need to cool off a grate, which is used in an incinerator, in a simple and effective manner while enhancing the cooling performance thereof.